The present invention concerns instrumentation and techniques for the treatment of spinal deformities. In particular, the inventive methods and devices accomplish this treatment without the need for fusion of the spine.
Surgical intervention for the treatment of injuries to, and deformities of the spine is approaching its first century. Nevertheless, the field of spinal surgery was not significantly advanced until the development of the hook and rod system by Dr. Harrington in the early 1950""s. Dr. Harrington developed this system in Houston when he began care of children with progressive neuromuscular scoliosis secondary to polio. Until that time, the progressive scoliosis had been treated with external casts, which themselves yielded unacceptably high complication rates. After a decade of development, the hook and rod system evolved into the form that is known today as the Harrington Instrumentation.
The original primary indication for use of Harrington Instrumentation was in the treatment of scoliosis. Scoliosis is a deformity of the spine in the coronal plane, in the form of an abnormal curvature. While a normal spine presents essentially a straight line in the coronal plane, a scoliotic spine can present various lateral curvatures in the coronal plane. The types of scoliotic deformities include thoracic, thoracolumbar, lumbar or can constitute a double curve in both the thoracic and lumbar regions.
Early techniques for correction of scoliosis utilized a halo-traction device. In this technique, a halo is fixed to the skull and a vertical force is applied to the spine through the skull. In a halo-femoral traction approach, the patient is supine and traction forces are applied through a halo and a femoral pin. In a halo-gravity traction procedure, the patient sits in a wheelchair and a suspended weight applies a vertical force through the halo. In halo-pelvic traction, a pelvic ring is affixed to the patient and a series of threaded rods connect the cranial halo to the pelvic ring to apply an adjustable force separating the two rings. In procedures using the halo, the patient is either immobile or severely restricted in mobility.
To avoid the need for halos, various rod-based systems have been developed. Of course, the original rod system for correction of scoliosis is the Harrington System which utilized threaded and notched rods. In particular, a typical Harrington System utilizes a notched distraction rod and at least one threaded compression rod, with the distraction and compression rods being applied to the concave and convex portions of the curvature, respectively. In some procedures, a single distraction rod spans across several thoracic and lumbar vertebrae. The threaded compression rods are then used to stabilize the rod fixation. In other approaches, the compression rod spans across the convex portion of the curve, such as between T6 and L2. In a Harrington procedure, a hook placed at the notched end of the distraction rod can be progressively advanced toward the cranial end of the rod to progressively correct the spinal deformation. At the same time, hooks engaged to the threaded compression rods can be drawn together on the convex side of the curvature to assist in the correction and to stabilize the instrumented spine.
In an additional step of the Harrington procedure, once the spine has been substantially corrected, transverse stabilization can be added between the two rods extending on opposite sides of the spine. Importantly, for long term stability, bone graft is placed along the instrumented vertebral levels to achieve fusion along that portion of the spine.
One drawback commonly associated with the Harrington System is that the rods are completely straight. As a result, patients in which a Harrington System has been used to correct a scoliosis condition have been left with the so-called flat-back syndrome. Specifically, in correcting the lateral curvature of the spine, the normal sagittal plane curvature is eliminated by the presence of a completely straight rod. In some cases, it has been found that the patient is better off retaining the scoliotic curvature than enduring the complications associated with flat-back syndrome. Another drawback is the requirement of bracing and casting.
To address these problems, subsequent rod-based systems have relied upon pre-bent spinal rods and multiple fixation sites. Specifically, the rods are bent to the normal thoracic kyphosis and lumbar lordosis in the sagittal plane. One such system is the Luque segmental spinal instrumentation. In the early 1980""s, Dr. Luque pioneered a technique for segmental correction of abnormal spinal curvatures in which wires were used to affix vertebral levels to a pre-bent rod. These sublaminar wires are used to help draw the vertebrae toward the rod and ultimately to hold the vertebrae in position. In one approach using Luque instrumentation, a unit rod is provided which utilizes a single rod anchored at its ends to the ilium and bent at its cranial end so that two halves of the rod are oriented on opposite sides of the spinal column. The unit rod can then be used as a lever to straighten the spine, after which Luque sublaminar wires are used to fix the vertebrae to the unit rod.
As with the Harrington System, the final step of the Luque Instrumentation is frequently fusion of the instrumented spinal segments. There have been suggestions for instrumentation without fusion to correct scoliosis in younger patients, this technique was believed to permit further spinal growth. However, the results of this instrumentation without fusion were not very promising and led to certain complications, including loss of correction, reduced spinal growth and an unacceptable rate of instrumentation failure.
In yet another rod-based instrumentation system pioneered by Dr. Cotrel in France, a pre-curved rod is engaged to the vertebrae at the concave side of the abnormal curvature. The rod is then rolled about its axis to derotate the scoliotic curvature and at the same time provide the instrumented segments with the normal sagittal plane curvature. For instance, in the correction of thoracic lordoscoliosis, rolling of a pre-curved rod not only derotates the curvature in the coronal plane, it also transforms that scoliotic curvature into a physiological thoracic kyphosis. The rod is held to the vertebrae by a series of hooks, which are ultimately fixed to the rod once the derotation process is complete. To ensure a stable correction, an additional rod is added on the opposite side of the spinous process from the first rod. Members for transversely connecting the two rods create a rigid scaffold are attached. Again, in this procedure, bone chips are placed along the instrumented vertebrae to achieve fusion at the instrumentation site.
Other rod-based systems have been developed over the last several years that accomplish similar correction of spinal deformities, such as scoliosis. For example, the TSRH(copyright) Universal Spine System of Danek Medical, Inc. and the ISOLA(copyright) Spine System of AcroMed Corp. can be instrumented to the spine to correct various types of spinal deformities. In all of these rod-based Systems, the spinal rods are permanently fixed to the patient""s spine. Of course, once fusion of all the instrumented levels has occurred, the original instrumentation is largely superfluous.
Other techniques that have been developed for correction of spinal deformities are performed anteriorly from the convex side of the abnormal curvature. In this technique, the intervertebral discs are removed and an osteotomy spreader is used to separate the adjacent vertebrae, thereby realigning the vertebral bodies in the coronal plane. A rod is attached to the spine via screws to maintain the correction. Fusion material, such as bone chips, are inserted into the widened intervertebral disc spaces to ultimately achieve fusion at those vertebral levels. Immobilization using an external cast or brace can be utilized while fusion is occurring.
A related technique involves Dwyer instrumentation that utilizes a flexible cable. In this technique, the cable is connected to the affected vertebrae on the convex side of the curvature. The cable is then shortened, thereby applying compression to the convex side of the curvature. Once the curvature has been corrected using the Dwyer cable, ancillary instrumentation, such as a Harrington rod, can be added for fixing and stabilizing the spine. In the Dwyer instrumentation, Dwyer clamps are pressed into the vertebral bodies to provide a seat for the insertion of Dwyer screws. The Dwyer screws define a channel through which the Dwyer cable can pass to perform the compression and ultimately the derotation of the abnormal curvature.
A similar approach is taken using Zielke instrumentation, except that the Dwyer cable is replaced by a pre-bent threaded rod. Application of the compressive forces to reduce the convex side of the curvature occurs by threaded nuts along the rod to translate the bone screws engaged to the vertebrae. Failed fusion because of residual deformity can be corrected by using posterior osteotomies which are closed and anterior wedges which are usually open. Following mobilization of the spinal segments by the osteotomies, then the spinal deformity can be corrected with instrumentation and then re-fused to maintain the correction.
While many techniques and instrumentation have been developed for the correction of spinal deformities, none of which we were aware prior to our invention, had been devised that could achieve the necessary correction without fusion of the instrumented vertebral levels. Moreover, some of the techniques resulted in an undesirable flat-back syndrome in which the normal sagittal plane curvature is eliminated. In addition, the prior systems greatly restrict the patient""s normal mobility, and some restrict the growth of the spine. In the latter instance, some of the spinal instrumentation is not acceptable for use in younger patients.
A need exists for a technique and system to correct spinal deformities without the necessity of fusing the corrected vertebral segments. A need also exists for a system and technique that can accomplish this correction with minimal long-term invasion of the patient.
In order to address these unmet needs, a method and instrumentation are provided for correction of spinal deformities without the need for fusion of the corrected segments. In one aspect of the invention, a surgical technique is provided in which osteotomies are closed on the convex side of the curvature deformity and opened on the concave side of the curvature. Mechanical wedges are engaged within the open wedge osteotomies on the concavity of the curvature. The vertebral bodies will heal and form a unified body at the location of the closed osteotomies. In this manner, the normal coronal plane position of the spine is restored by elimination of the curvature deformity.
In a further aspect of the technique, the orientation of the opening or closing wedge osteotomies can be predetermined to achieve a normal curvature in the sagittal plane and normal spinal orientation in the coronal plane. For example, the addition of mechanical wedges into opening wedge osteotomies in the lumbar spine can be used to eliminate an abnormal lateral curvature while restoring the normal lordotic curvature of the lumbar vertebrae.
In a further aspect of the technique, connection elements or fasteners are engaged to each of the vertebrae in which an osteotomy has been performed. The connection element can then be engaged to an elongated member, such as a spinal rod, that has been pre-bent to the adjusted spinal curvature. The longitudinal member stabilizes the spine as the closing osteotomies heal and the mechanical wedges become integrated into the vertebrae having the opening wedge osteotomies. In this manner, the intervertebral discs are maintained intact. Moreover, and perhaps most significantly, none of the vertebral levels are fused together. Once the vertebral bodies have completely healed, the longitudinal member can be removed. With this feature of the inventive technique, the normal mobility of the patient""s spine is restored since the intervertebral discs are not fused.
In another aspect of the invention, instrumentation is provided that can be used to perform the inventive technique. In one feature of the invention, the instrumentation includes a correction device that includes upper and lower anchors configured to penetrate a single vertebral body at substantially opposite sides of the body. In three illustrated embodiments of the instrumentation, the anchors are in the form of staples. In other illustrated embodiments, the anchors are in somewhat the form of a half staple or an adz. In all illustrated embodiments, a connection element is provided that extends between the upper and lower anchors and through the vertebral body. In one implementation, the connection element includes a threaded shank that engages a mating threaded boss on the lower anchor. In another implementation, the connection element has a threaded shank which is fixed to the lower anchor, and a head portion of the instrumentation is threaded onto the shank. In both implementations, the connection element can be used to provide a compressive force between the upper and lower anchors, thereby retaining their position and engagement with the vertebral body.
In the various implementations, the connection element includes a head portion adjacent the upper anchor. The head portion can be configured for connection to an elongated member used to stabilize the spine. In one embodiment, the head of the connection element is configured to engage an elongated spine rod. In another, it is configured for a spinal tethering function.
In accordance with a further feature of the invention, two types of correction devices can be provided. One correction device is utilized to close the closing wedge osteotomy in a vertebral body. In this correction device, the connection element is used to engage an upper and lower anchor to the vertebral body. In the second correction device, a mechanical wedge is attached to the lower anchor. The second correction device is thus used in maintaining the opened wedge osteotomies on the concavity of the curvature to be corrected. The mechanical wedge member is situated within the open space created by the opening wedge osteotomy. The anchors, stabilize the opening wedge osteotomy in a closing direction around the mechanical wedge as the vertebral body heals. In some mild cases, adequate correction may be achieved without intervertebral rods, plates, cabling or tethering, and a further embodiment of the invention for such cases, is disclosed.
In accordance with the present invention, a method is provided for correcting spinal deformities without the need ion fusion of the spine. A further object of the invention is accomplished by the technique and instrumentation that allows a stabilizing elongated member to be used only temporarily. This aspect provides the benefit that the elongated member, such as the spinal rod, can be removed once the instrumented vertebrae have healed, thereby restoring the normal mobility to the patient""s spine.
Another object of the present invention is achieved by aspects of the technique and instrumentation that allows for adjustment of the spinal curvature in both the sagittal and the coronal planes. Still other objects and certain benefits of the invention will be discerned from the following written description of the invention together with the accompanying figures.